1. Field of the Invention
The field of this invention relates to polyamide-imide-phthalamide copolymers containing polyetherimides, to molding powders, molded articles and to films prepared therefrom.
Amide-imide polymers are a relatively new class of organic compounds known for their solubility in nitrogen-containing organic solvents when in the largely polyamide form. The major application of the amide-imide copolymers has been as wire enamels. This is illustrated in U.S. Pat. Nos. 3,661,832, (1972), 3,494,890 (1970) and 3,347,828 (1967).
Compositions prepared from isophthalic acid and diamines and aliphatic diamines have found application in coatings and films. The prior art on this is summarized in U.S. Pat. No. 3,444,183 (1969).
Reinforced polyhexamethylene isophthalamides have been used to produce articles as disclosed in U.S. Pat. No. 4,118,364 (1978). However, the physical properties of these reinforced polyhexamethylene isophthalamides are insufficient for use in engineering plastics, since their tensile strength and the continuous service temperature does not meet those required for engineering plastics.
Polyamide-imide-phthalamide copolymers are extremely rigid polymers which lack the inherent toughness needed to compete in those applications which require elevated temperature resistance and good impact strength. The lack of matrix toughness can cause problems when molding thick cross-sectional parts, especially with the filled copolymers, since the copolymer matrix is not strong or tough enough to resist the molding cool down stresses which can result in internal cracks. The art has been looking for improvements in the impact resistance and toughness of the polymer, but it is essential that the additive not impair the excellent curing characteristics of the PAI or its thermal and strength properties, particularly the heat deflection temperature and tensile strength.
The general object of this invention is to provide polyamide-imide-phthalamide copolymers containing polyetherimides. A more specific object of this invention is to provide polyamide-imide-phthalamide copolymers suitable for use as engineering plastics and particularly for use in injection molding wherein the physical properties of the copolymers are improved by the addition of about 0.1 to about 50 percent by weight of polyetherimides. Other objects appear hereinafter.
I have now found that amide-imide-phthalamide copolymers obtained in reacting a polycarboxylic acid anhydride and a dicarboxylic acid with primary diamines or a mixture of primary diamines, comprising about 0.1 to about 50 percent by weight of polyetherimide, have excellent physical properties and can readily be injection molded to provide engineering plastics with excellent properties. The polyetherimides improve the physical properties and reduce mold part cracking of neat or filled amide-imide-phthalamide copolymers and also when glass fibers, glass beads, mineral fillers, graphite fiber or graphite powder are coated with the polyetherimides, these can more readily be incorporated into a molded amide-imide-phthalamide object. Polyetherimides have also been found to aid the manufacture of amide-imide-phthalamide films having a thickness of about 0.5 to about 10 mils. Films without polyetherimides are so brittle that they cannot be prepared from amide-imide-phthalamide copolymers having a thickness of about 0.5 to about 10 mils without cracking and tearing.
Suitable polyetherimides comprise essentially chemically combined units of the formula: ##STR1## where R is a member selected from the class consisting of (a) the following divalent organic radicals: ##STR2## and (b) divalent organic radicals of the general formula: ##STR3## where X is --C.sub.y H.sub.2y --, y is a whole number equal to 1 to 5 inclusive, and R.sup.1 is a divalent organic radical selected from the class consisting of (a) aromatic hydrocarbon radicals having from 6-20 carbon atoms and halogenated derivatives thereof, (b) alkylene radicals and cycloalkylene radicals having from 2-20 carbon atoms, (c) C.sub.(2-8) alkylene terminated polydiorganosiloxanes, and (d) divalent radicals included by the formula: ##STR4## where Q is a member selected from the class consisting of: ##STR5## and x is a whole number equal to 1 to 5, inclusive.
We have unexpectedly discovered that blends of polyamide-imide-phthalamide copolymers and polyetherimides disclosed herein over a wide range can be made in which the properties of the blend show a marked average improvement over the properties of the components of these blends, and in some instances, the improvements in properties are unexpected, considering the proportion of either the polyamide-imide or the polyetherimide used. By making the above-described blends, the utility for both these members in the blend can be considerably expanded. In addition, by blending the polyamide-imide with polyetherimides, products can be obtained which are lower in cost than is usually associated with the use of the polyamide-imide alone without significant sacrifice, if any, in thermal properties.
The polyetherimides which are employed in the present invention can be made in accordance with the disclosures and teachings in U.S. Pat. No. 3,847,867 issued Nov. 12, 1974. The polyamide-imide employed in the practice of the instant invention can also be made in accordance with the disclosures and teachings in U.S. Pat. Nos. 4,313,868 and 4,309,528. By reference, these patents are made part of the disclosures and teachings of the instant application.
The amide-imide copolymers comprise recurring polyamide A units of: ##STR6## which are capable of undergoing imidization, and polyamide B units of: ##STR7## wherein the molar ratios of A units to B units is about 80 to 20 to 20 to 80, preferably 1 to 1 and wherein R is a divalent aromatic hydrocarbon radical of from about 6 to about 20 carbon atoms or two divalent hydrocarbons joined directly or by stable linkages selected from the group consisting of --O--, methylene, --CO--, --SO.sub.2 --, and wherein X is a divalent aromatic radical and .fwdarw. denotes isomerization.
In the injection molded form, the polyamide A units have converted to the polyamide-imide A' units and the copolymer comprises recurring polyamide-imide A' units of: ##STR8## and polyamide B units of: ##STR9## wherein the molar ratio of A' and B units is about 80 to 20 to about 20 to 80, preferably about 1 to 1 and wherein R and X are defined as above.
The copolymers of this invention are prepared from acyl halide derivatives of dicarboxylic acid such as isophthalic acid or terephthalic acid and an anhydride-containing substance and aromatic diamines. Useful acyl halide derivatives of dicarboxylic acid include: ##STR10## and related compounds. Suitably, the anhydride containing substance is an acyl halide derivative of the acid anhydride having a single benzene or lower acyl substituted benzene ring. The preferred anhydride is the four acid chloride of trimellitic anhydride (4 TMAC).
Useful aromatic diamines include para- and meta-phenylenediamine, oxybis (aniline), thiobis (aniline), sulfonylbis (aniline), diaminobenzophenone, methylene-bis (aniline), benzidine, 1,5-diaminonaphthalene, oxybis(2-methylaniline), thiobis(2-methylaniline), and the like. Examples of other useful aromatic primary diamines are set out in U.S. Pat. No. 3,494,890 (1970), and U.S. Pat. No. 4,016,140 (1977) both incorporated herein by reference. The preferred diamine is meta-phenylenediamine.
The copolymers of this invention are prepared by reacting a mixture of an acyl halide derivative of an aromatic tricarboxylic acid anhydride and acyl halide derivatives of aromatic dicarboxylic acids with aromatic diamines.
A preferred class of polyetherimides which are included by formula (III) are polymers comprising of from about 2 to 5000 or more units and preferably from about 5 to about 100 units of the formula: ##STR11## where R.sup.1 is previously defined, and R.sup.2 is: ##STR12##
Included by the polyetherimides of formula III, are polymers comprising the following chemically combined units: ##STR13## and mixtures thereof, wherein R.sup.1 and R.sup.2 are defined above.
The polyetherimides of formulas III-VI can be made by effecting reaction between an aromatic bis(etheranhydride) of the general formula: ##STR14## and an organic diamine of the general formula EQU H.sub.2 NR.sup.1 NH.sub.2 (VIII)
where R and R.sup.1 are as previously defined.
There can be employed from 0.95 to 1.05 mols of aromatic bis(etheranhydride) per mol of organic diamine.
In making the polyetherimides, there are employed from 0.95 to 1.05 mols of the aromatic dianhydride of formula VII per mol of the organic diamine of formula VIII. Preferably, one can employ equal or lower amounts of the bisanhydride and diamine.
The aromatic bis(etheranhydride) of formula VII shown in the above-mentioned U.S. Pat. No. 3,847,867, can be prepared from the hydrolysis followed by dehydration of the reaction product of the nitrosubstituted phenyl dinitrile and then continuing the reaction with a dialkali metal salt of a dihydric aryl compound in the presence of a dipolar aprotic solvent, where the alkali metal salt has the general formula EQU Alk--O--R.sup.1 --O--Alk
where R.sup.1 has the meanings given above and preferably is the same as R.sup.2 and Alk is an alkali metal ion. Various well-known procedures can be used to convert the resulting tetranitriles to the corresponding tetracids and dianhydrides.
The amount of the polyetherimide added to the polyamide-imide-phthalamide copolymer can be about 0.1 to about 50 weight percent, usually in the range of about 10 to about 40 weight percent.
The addition of these polyetherimides increases the physical properties as follows:
TABLE I ______________________________________ Sample A B C D E ______________________________________ Polyamide-imide, % 96.5 87 77.5 67.5 58 Polyetherimide, % -- 9.5 19 29 38.5 TiO.sub.2, % 3.0 3.0 3.0 3.0 3.0 PTFE, % 0.5 0.5 0.5 0.5 0.5 Blend Ratio PAI/PEI 100/0 90/10 80/20 70/30 60/40 Physical Properties Tensile Strength .times. 10.sup.3 PSI As-Molded 3.0 6.8 5.3 7.8 9.7 Cured @ 500.degree. F. -- 12.6 17.4 20.5 -- Cured @ 515.degree. F. 16.6 23.8 22.8 21.6 19.8 Tensile Elongation, % As-Molded 1.4 2.6 1.8 2.3 4.6 Cured @ 500.degree. F. -- 4.8 6.4 7.4 -- Cured @ 515.degree. F. 5.8 8.2 9.2 10.0 9.3 Flexural Modulus .times. 10.sup.6 PSI As-molded 0.75 0.52 0.55 0.55 0.64 Cured @ 500.degree. F. -- 0.64 0.63 0.61 -- Cured @ 515.degree. F. 0.84 0.65 0.63 0.59 0.54 Izod Impact, Notched ft-lbs/in As-Molded * 0.2 0.5 0.5 0.1 Cured @ 500.degree. F. -- 0.9 0.8 1.4 -- Cured @ 515.degree. F. 0.4 0.8 1.3 1.5 1.2 Dart Impact, in-lbs &lt;2.0 -- 22.6 -- -- Cured @ 515.degree. F. HDT, .degree.F. As-Molded 475 482 468 437 403 Cured @ 500.degree. F. -- 540 539 526 -- Cured @ 515.degree. F. 553 563 540 542 -- ______________________________________ *Sample broke during notching (sample preparation)
TABLE II ______________________________________ Sample F G H I ______________________________________ Polyamide-imide, % 59 53 47 55 Polyetherimide, % -- 6 12 14 Glass Fibers PPG 3540, % 40 40 40 -- Graphite Fibers AS1810, % -- -- -- 30 PTFE, % 1 1 1 1 Blend Ratio PAI/PEI 100/0 90/10 80/20 80/20 Physical Properties Tensile Strength .times. 10.sup.3 PSI As-Molded 10.8 20.8 19.7 21.8 Cured @ 500.degree. F. 29.0 33.3 32.7 38.0 Tensile Elongation % As-Molded 2.0 3.2 3.0 6.2 Cured @ 500.degree. F. 6.0 7.2 6.9 8.8 Flexural Modulus .times. 10.sup.6 PSI As-Molded 2.1 2.0 2.0 2.59 Cured @ 500.degree. F. 2.0 1.9 1.9 2.46 Flexural Strength .times. 10.sup.3 PSI As-Molded 25.2 35.6 31.9 31.7 Cured @ 500.degree. F. 51.4 56.1 53.7 56.8 Izod Impact, Notched ft-lbs/in As-Molded 1.0 1.6 1.5 0.9 Cured @ 500.degree. F. 1.6 1.8 2.0 1.3 Dart Impact, in-lbs 4.5 -- 10.5 -- Cured @ 500.degree. F. HDT, .degree.F. As-Molded 500 512 507 494 Cured @ 500.degree. F. 550 555 552 550 ______________________________________
Polyamide-imide-phthalamide polyetherimide copolymers build their properties during the annealing step such that molded properties are significantly below the annealed properties as shown in Table 3. To build polyamide-imide-phthalamide polyetherimide properties, parts are annealed at temperatures up to about 530.degree. F. but preferably about 500.degree. to about 520.degree. F. It is important that the polyamide-imide-phthalamide Tg is maintained above the maximum annealing temperature such that optimum properties can be built during annealing. It is also important that the polyamide-imide-phthalamide Tg is above the maximum annealing temperatures so that part distortion due to stress relaxation does not occur.
TABLE III ______________________________________ As Annealed Molded at 500.degree. F. ______________________________________ Glass Loading, % 40 40 Injection Molding Temp., .degree.F. 650 650 Physical Properties Tensile Strength, psi 10,800 29,000 Tensile Elongation, % 2.0 6.0 Flexural Modulus, psi 2,100,000 2,000,000 HDT, .degree.F. 500 550 ##STR15## 1.0 1.6 ______________________________________
After cure, a representative 20 percent polyetherimide neat polyamide-imide-phthalamide copolymer sample had total shrinkage of 10 mils per inch, while the control had a shrinkage of 8 mils per inch.
It should be particularly emphasized that when our polyamide-imide-phthalamide copolymers are blended with polyetherimides, an ideal two-phase system is formed giving two specific glass transition temperatures, one at about 270.degree. C. and the other at about 215.degree. C.
Polyamide-imide-phthalamide-polyetherimides coated on sized fillers such as glass fibers give better molding characteristics and improved as-molded properties. Thus polyamide-imide-phthalamide-polyetherimide copolymers, containing about 20 to about 60 percent fillers can be marketed without loss of the excellent cured thermal properties of our polyamide-imide-phthalamide copolymers.
Cavity pressure measurements are used as quality control checks of polyamide-imide-phthalamide-polyetherimide resin viscosity. Pressure buildup during the filling of an injection molded part is measured at a point in the cavity (ejector pin). This is accomplished by placing a pressure transducer behind the ejector pin and recording the pressure with a chart recorder or other readout device. Cavity pressure normally rises as the mold is being filled and peaks as the molten resin is packed into the cavity. As the resin solidifies, cavity pressure decreases.
We have found that resins that have low cavity pressure process poorly and that spiral flow measurements were not sensitive enough to discriminate between resins in the viscosity range of interest. Low cavity pressures indicate a large pressure drop between injection and cavity pressures. This indicates higher resin viscosities. In the same manner high cavity pressures indicate less pressure change between injection and cavity pressures, suggesting lower resin viscosities.
Amide-imide polymer and copolymer viscosities had been measured by spiral flow determination previous to the implementation of the cavity pressure procedure, see U.S. Pat. No. 4,224,214. Cavity pressure was selected over spiral flow because of its greater sensitivity. The cavity pressure test has been implemented as an amide-imide homopolymer and copolymer quality control procedure. Like spiral flow, cavity pressure is a test that can be done conveniently in a molder's shop.
The injection molding machine was equipped with a horizontally mounted thermoset screw and barrel assembly. The mold was heated with hot oil from a Mokon Model 105-057 heating unit. Cavity pressure was recorded with a Control Process Model 241 recorder. The mold was equipped to handle pressure transducers at the ejector pins located at the gate end of the tensile bar and the gate end of the flex bar before beginning the work. Since it was desirable to make cavity pressure measurements at the dead end of the flex bar, it was necessary to make some modifications in the mold base to accommodate a transducer at this pin position.
Resins were dried in a desiccant hot air circulating oven at 300.degree. F. for at least 16 hours before testing. Moisture in polyamide-imide-phthalamide-polyetherimide system has a very significant effect on the copolymers and their flow properties. Therefore, special care was taken to be sure the samples were properly dried. This drying procedure was used before making flow rate and cavity pressure measurements.
The flow rate procedure was patterned after the standard method described in ASTM D1238. A 335.degree. C. (635.degree. F.) barrel temperature with a 30 minute preheat time was used. This is about the largest set of weights that can be used safely with the standard extrusion plastometer apparatus. A standard 0.0825 in. diameter, and a 0.315 in. long orifice was used.
Special care was taken to be sure that each flow rate measurement was started when an equivalent volume of resin was in the barrel. Previous rheology work indicated that there is a very large "barrel height" effect on amide-imide copolymers. Each flow rate measurement was initiated while the top of the piston collar was between the two scribe marks on the piston. This precaution is also required by ASTM in method D1238.
Films having a thickness of about 0.5 to 10 mils have been produced from our polyamide-imide-phthalamide-polyetherimide resins. These films have properties as shown in Example 15.
The reinforced polyamide-imide-phthalamide-polyetherimide copolymers may be prepared in various ways. For example, so-called roving endless glass fiber strands are coated with the polyetherimide, disclosed herein, and then are further coated with the polyamic acid melt and subsequently chopped. The chopped fibers or the glass beads coated with polyetherimides may also be mixed with granulated polyamic acid and the resulting mixture melted in a conventional extruder, or alternatively the fibers coated with polyetherimides may be directly introduced into the polyamic acid melt through a suitable inlet in the extruder. Injection molding of the unfilled or glass-filled polyamide-imide-phthalamide-polyetherimide copolymers is accomplished by injecting the copolymers into a mold maintained at a temperature of about 350.degree. F. to about 450.degree. F. In this process, a 15 to 30 second cycle is used with a barrel temperature of about 580.degree. F. to about 670.degree. F. The injection molding conditions are given in Table IV.
TABLE IV ______________________________________ Set Points ______________________________________ Cylinder Temperatures, .degree.F. Nozzle 650-670 Front Zone 650-670 Rear Zone 640-660 Timer, seconds Clamp Closed (cure) 18 Injection Hold 6 Booster (Inj. Hi) 2 Cycle Delay (open) 1 High-Low 2 Injection Pressure, psi High 20,000 Low 10,000 Machine Settings Clamp Pressure, tons Max. Injection Rate Max. Screw RPM 50 Feed Setting As Req'd. Cushion 1/4" Back Pressure, psi 220 Mold Temperature, .degree.F. Stationary 450 Movable 450 Hopper Drier 220 ______________________________________
The mechanical properties of the unfilled amide-imide copolymers containing polyetherimides (melt compounded) and also the filled polyamide-imide-phthalamide polyetherimide copolymers are given in Table V and it shows that these copolymers have improved cured mechanical properties and excellent thermal properties despite the fact that they contain about 10 to about 40 weight percent of polyetherimides.
TABLE V __________________________________________________________________________ Polyamide-imide, % 96.5 87 77.5 67.5 58 59 53 47 Polyetherimide, % 0 9.5 19 29 38.5 -- 6 12 TiO.sub.2, % 3.0 3.0 3.0 3.0 3.0 -- -- -- PTFE, % 0.5 0.5 0.5 0.5 0.5 1 1 1 Glass Fibers -- -- -- -- -- 40 40 40 PPG 3540, % Blend Ratio 100/0 90/10 80/20 70/30 60/40 100/0 90/10 80/20 Tensile Strength 16.6 23.8 22.8 21.6 19.8 29.0 33.3 32.7 .times. 10.sup.3, PSI Tensile Elongation, % 5.8 8.2 9.2 10.0 9.3 6.0 7.2 6.9 Flexural Strength -- 31.4 31.4 30.4 31.5 51.4 56.1 53.7 .times. 10.sup.3, PSI Flexural Modulus 0.84 0.65 0.63 0.59 0.54 2.0 1.9 1.9 .times. 10.sup.6, PSI ##STR16## 0.4 0.8 1.3 1.5 1.2 1.6 1.8 2.0 Dart Impact, in.-lbs. &lt;2.0 -- 22.6 -- -- 4.5 -- 10.5 HDT, .degree.F. 553 563 540 542 -- 550 555 552 Flexural Strength 24.8 -- -- 18.8 -- 36.1 39.9 35.5 .times. 10.sup.3, PSI @ 400.degree. F. Total Shrinkage, 8.0 10.0 10.0 10.0 17.5* 1.0 1.0 1.0 mils/in. __________________________________________________________________________ Neat samples were cured @ 515.degree. F.; the fiber filled samples cured 500.degree. F. *Sample distorted when cured @ 515.degree. F.
All of the materials studied were molded on the 10 oz. Stokes injection molder under Table IV molding conditions unless specified otherwise. A 10 oz. Stokes injection molder is fitted with a 1:1 compression thermoset screw which can hold approximately 365 grams of the polyamide-imide-phthalamide-polyetherimide-copolymer (approximately 0.8 lbs). Since each test tree weighs approximately 23 grams (neat parts) only 1/16th of the complete injection stroke (shot volume) is used during the molding evaluation. Under these conditions (18 second clamp), the total time the copolymer is trapped in the barrel is approximately 7.2 minutes (total cycle is 27 seconds). This does not mean that the copolymer is in the melt state for the complete 7.2 minutes due to the temperature gradient (front to rear) in the barrel. For a complete material transition (purge) 16-20 shots must be taken before collecting data.
Polyamide-imide-phthalamide-polyetherimide copolymer flow, under molding conditions, is determined by its cavity pressure which is measured at a point farthest from the sprue. In this test, a pressure transducer is fitted behind a knockout point located behind the flex bar. The higher the cavity pressure, the better the flow thus making for easier mold filling. To determine our polyamide-imide-phthalamide-polyetherimide copolymer reactivity a plot of cavity pressure vs. cycle time is drawn. A stable or non-reactive resin will exhibit good flow characteristics under adverse molding conditions resulting in a melt insensitive to a change in cycle time. A reactive copolymer will be cycle time dependent in that its viscosity increases with cycle time. This is illustrated by a steep negative cavity pressure slope. Polyamide-imide-phthalamide-polyetherimide copolymer samples were all dried for approximately 16 hours at about 300.degree. F. in a hot air circulating oven containing a suitable desiccant. Polyamide-imide-phthalamide-polyetherimides were dried overnight in a vacuum oven at 230.degree. F. Samples were dry blended together and stored under vacuum in sealed containers.
Polyamide-imide-phthalamide-polyetherimide copolymer samples were cured in a Blue M hot air programmable oven under a 7-day cycle with 1 day at 320.degree. F., 400.degree. F., 450.degree. F., 475.degree. F. and 3 days at 500.degree. F. Several tensile bars were cured under a 7-day cycle with 3 days at 515.degree. F.
The following examples illustrate the preferred embodiment of the invention. It will be understood that the examples are for illustrative purposes only and do not purport to be wholly definitive with respect to conditions or scope of the invention.